1. Technical Field
The techniques described herein relate to a process for constructing heat exchangers using low temperature sinter techniques and the heat exchangers that result from the process.
2. Discussion of Related Art
Heat exchangers are used in a variety of applications, for example, cooling engines and cooling electronics. Techniques for constructing heat exchangers include brazing and organic bonding.
Brazing may be performed, for example, in a molten salt bath or in a vacuum furnace and requires very high temperatures (from 300° C. to 1100° C.). These high temperatures melt a brazing material, such as metals or compatible alloys (e.g. aluminum alloys), that is in contact with two or more other pieces of metal that are part of the heat exchanger. Upon cooling, the brazing material solidifies, forming a bond that thermally, and physically, couples the metal pieces together. The high temperature needed for brazing places limits on the heat exchangers being constructed. For example, the material used to make the heat exchanger must have a melting point higher than the brazing temperature. Moreover, the large temperature variation, from room temperature to the brazing temperature and back, require the materials that are chosen to have similar coefficients of thermal expansion (CTE). If the heat exchanger was constructed from metal with a large difference in CTE, the heat exchanger could break, warp or have unwanted residual stress upon cooling to room temperature. Limitations are also put on the choice of material based on the need to reduce galvanic corrosion.
Another restriction of brazing is that it typically requires special equipment, such as a molten salt bath or a vacuum furnace. Therefore, the brazing process requires purchasing expensive, specialized equipment or contracting an off-site brazing specialist, which can be both unaffordable and time-consuming, with lead times of greater than 16 weeks.
One alternative to brazing is organic bonding using a polymer bond solution. While this technique is much cheaper than brazing, the materials used to form the bond have a much higher thermal resistance than the brazing materials. For example, typical polymer bond solutions have a conductivity that is about 100 times lower than copper or silver. This reduction in conductivity reduces the ability to dissipate heat and results in reduced performance of the underlying device.